Method for locating points on a three-dimensional surface using light intensity variations

ABSTRACT

A method for locating points on a surface in which the surface is irradiated selectively with an irradiating volume which has a varying intensity that defines a first pattern. After irradiating the surface with the first pattern, the surface is irradiated similarly with volumes having varying intensities defining a second or more patterns. Both of these patterns are applied to a point to be located on the surface. The radiation impinging on the surface is recorded by a camera which forms images of the patterns. The images are scanned to find the intensities of the point in the two or more patterns. More than one pattern may be simultaneously irradiated, using different frequencies to distinquish the data. The location of the point on the surface is dependent on a predetermined ratio or difference of the intensities of the point in the two or more patterns. The patterns may be linear, sinusoidal, smooth, non-smooth and/or two dimensional functions ultimately producing a single valued ratio or difference result.

BACKGROUND OF THE INVENTION

This application is a continuation-in-part of the copending applicationSer. No. 432,267 filed Oct. 1, 1982.

The present invention is concerned with a method for defining athree-dimensional object in space by locating points on the surface ofthat object. The three-dimensional locations of the points aredetermined by irradiating the surface with varying light intensities andmeasuring the differences and/or ratios of the light intensities.

In the past, the three-dimensional locations of points on a surface wasachieved using digital methods which are described in a number ofrelated patents. In the present invention, analog irradiated lightpatterns are used with or without such previous digital methods. Theanalog irradiated light patterns used in the present invention allow forinfinitesimal resolution in finding the locations of points on asurface, in contrast with the previous digital methods in which theresolution was limited to a predetermined discrete section or area.

RELATED CROSS-REFERENCES

The follow U.S. Patents may be referred to for development of the artfor locating points on a three-dimensional surface:

U.S. Pat. Nos. 4,145,991, 3,866,052, 4,175,862, 4,185,918, 4,259,589,4,269,513.

SUMMARY OF THE INVENTION

It is an object of the present invention to define the locations ofpoints on a three-dimensional surface using light patterns of varyingintensities to analyze the surface.

Another object of the present invention is to provide the foregoingmethod with analog irradiated light patterns which may be used with orwithout digital methods of the prior art.

A further object of the present invention is to provide a method asdescribed, in which the analog light patterns allow for infinitesimalresolution in determining the location of the points on a surface.

The objects of the present invention are achieved by irradiating asurface selectively with patterns of light having varying intensities.In any pattern of light the varying intensities define a first pattern.

After the surface has been irradiated with the first pattern, the samesurface is subjected to a second irradiating pattern having varyingintensities defining a second pattern. The two patterns are arranged sothat when superimposed on one another they will form into sections. Apoint on the surface is uniquely located by correlating the two patternswith respect to the point.

Images of the patterns are recorded by a camera, and these images arescanned to find the light intensities of the point in the two patterns.By noting the relative intensities of the point and forming a ratio ofthe two intensities, the projector angle of the point may be uniquelydefined. The projector angle of the point can also be defined by takingdifferences (i.e., subtractions) of the two light intensities of thepoint in the two patterns provided that the reflectivity of the measuredsurface is sufficiently uniform to provide the data to the accuracyrequired. Once the projector angle is known, methods of the prior artmay be employed to solve for the 3-D position of the point.

The novel features which are considered as characterisitic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic top (plan) view of an arrangement in which asurface is analyzed by the application of volumes of light of varyingintensities, in accordance with the present invention;

FIG. 1A is an isometric view of light volumes expressing intensities andprojector shown in FIG. 1;

FIG. 2 is a graphical representation of linear light intensityfunctions, and the measurement of these functions to obtain locatinginformation for a point on the surface;

FIG. 3 is a graphical representation of non-smooth functions which maybe used in the method of the present invention;

FIG. 4 is a graphical representation of sinusoidal functions which maybe used in the method of the present invention;

FIG. 5 is a graphical representation of the use of a sinusoidal functionin combination with a linear function in the method of the presentinvention;

FIG. 6 is a graphical representation of the use of a digital function incombination with a linear function in the method of the presentinvention;

FIG. 7 is a drawing depicting a method of generating volumes of lightwith intensity varying linearly in the horizontal direction as shown inFIGS. 1 and 1A;

FIG. 7A is a graphical representation of integrated light as a functionof horizontal position in projected pattern under condition of rotatingmask regions;

FIG. 7B is a graphical representation similar to FIG. 7A under anothercondition of rotating mask regions;

FIGS. 8A and 8B are graphical representations of a multiplevaluedpattern that can be used for the fine grain resolution when seen fromtop or plan view; and

FIG. 9 is an isometric view of a light volume whose intensity varies intwo directions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, the surface 12 of an object 10 is irradiatedwith volumes of light 14 emitted by a projector 16. (Reference FIGS. 1and 1A). A camera 18 records images of the volumes of light as theyimpinge on the surface 12.

To illustrate that the intensity of light within the impinging volume 14varies throughout this volume, the edge 20 of this volume facing theobject 10 has been given an inclination as shown in FIGS. 1 and 1A. Theinclination is intended, for example, to represent that the lightintensity varies from low intensity at the edge 22 to high intensity atthe edge 24. In the configuration shown in FIGS. 1 and 1A, the varyingintensity of the pattern is denoted to be a linear or straight-linevariation 20.

If only one such light volume 14 is applied to the surface 12 anddirected to a point 11 thereon, the location of the point is notuniquely defined. In order to obtain unique results, it is essential toirradiate the same point on the surface with another volume of light 26illustrated by dashed lines in FIG. 1 and FIG. 1A.

The intensity variation of the volumes 26 is made opposite to the volume14. This is represented by the edge shown in dashed lines 28. Thus,whereas the intensity is low along edge 22 in volume 14, the intensityin volume 26 is high along edge 22, and conversely the intensity is lowin volume 26 along line 24 in contrast to the high intensity in volume14.

When the light intensity variations represented by 20 and 28 aregraphically plotted, they appear as shown in FIG. 2. If the point 11 tobe located lies at the angle 30 along the surface, then the projectorangle of this point is uniquely determined by taking the ratio A/B. Thisangle applied with the prior art is sufficient to calculate the 3-Dlocation of the point. Depending on the character of the surface, thedifference between these two parameters, A-B, may also be taken toobtain the angular location of the point.

Thus, in the arrangement of FIGS. 1, 1A and 2, the projector applies twostraight lined or "proportional" signals in sequence on the surface tobe analyzed. Assuming the absence of room light or cross talk, the ratioof the light intensities at a point on the three-dimensional objectilluminated by the two projector outputs, is an indication of the angleof measurement plane (or ray) emanating from the projector. Thisprojector angle is used as in the digital methods of the prior art tocalculate the three-dimensional position of the point 11 on the surface.

It is not essential that the projector output signals have uniformslopes although the method, when employing horizontal variation ofintensity and intensity differences to determine the projector angle, isadversely affected by vertical intensity variation. Instead, it isnecessary only that the emitted intensities have calibratedsingle-valued ratios or differences. The ratios or differences of thetwo intensities that are measured may then be referred to in acalibrated reference table to obtain the angle. Ratio measurements arenot affected by surface reflectance or vertical intensity variation ifthe various light patterns contain the same spectral composition andemanate from a single projector node.

It is necessary to have single valued functions to obtain uniquelocations. However, as in the prior art, multiple valued patterns can beused for fine grain resolution and the ambiguity of multiplicityresolved by coarser grain patterns. An example of such a pattern may beas that given in FIGS. 8A and 8B. The ratios obtained from measurementsin the rapidly varying regions such as at 80 and 81 give high angularsensitivity for high resolution measurement.

If the room light is present on the object being analyzed, a third imagemay be taken by the camera and the room light intensity as recorded bythat image may be subtracted from the previous two intensities A and Bin FIG. 2 to obtain the desired ratio as follows: ##EQU1##

Whereas, the taking of ratios of intensities will produce the necessaryresults in defining uniquely the projector angle to a point in space, itis also possible to take only the differences of the intensities in somecases, depending on the geometrical character of the surface beinganalyzed. However, the method in which ratios of the intensities aretaken will produce generally superior results to the method in which thedifferences of intensities are taken.

It is necessary to have a surface that does not introduce falsedifference information if only differences of intensity are to be used.For example, rapidly varying surface reflectivity (from texture, color,angle of incidence, etc.) will introduce false difference values.However, it may still be possible to extract information, although mostlikely of less accuracy.

The method of the present invention may also be used with a projector inwhich two or more calibrated color signals are used. Such a methodprovides for increased speed in analyzing a surface, and may providealso for mechanical simplicity.

The increased speed may be obtained by parallel processing. The multiplecolors may be projected simultaneously and separated by filters at thecamera(s) to obtain the separate pattern information.

As already noted, it is not essential that the light intensity patternprovide a linear pattern 20 and 28 as shown in FIGS. 1 and 1A. Instead,the light pattern may, for example, be used as shown in FIG. 3. In thearrangement of FIG. 3 the light intensity pattern 32 has a sharplyvarying contour 36 in contrast to the linear or proportional contour 20.In conjunction with the volume 32, the second volume 34 is provided witha pattern 38 which is precisely the inverse of the pattern 36 forsimplicity. The second volume of light need not be the inverse of thefirst pattern.

Thus, as shown by FIG. 3, it is not essential that the projector outputbe a smooth function. In general, any function can be used provided ithas a ratio which is a single-valued function.

Smooth functions are generally easier to deal with than functions thatare not smooth as shown in FIG. 3, and accordingly sinusoidal functionsshown in FIG. 4 are applicable for this purpose. In FIG. 4, for example,the first intensity pattern is represented by the sinusoidal wave 40,whereas the inverse intensity pattern is represented by the sinusoidalwave 42. (In this case A and B become equal several times at crossingpoints and beyond 2π angle. The two waves can also be arranged so thatone wave has a period which is either longer or shorter than the otherwave. The projector angle of the point at a position 30 along thesurface is again determined by the ratio A/B.

Thus, sine and cosine waveforms may be used in various combinations toobtain the desired results.

It is also possible to use a sinusoidal wave pattern in the firstvolume, a linear intensity pattern in a second volume and a constantamount of light in a third volume as shown in FIG. 5 by the waveforms44, 46 and 50, respectively.

In this case the projector angle can be found by using ratios A/C andB/C as found in FIG. 5 as address arguments for finding projector anglein a look up table.

It is also possible to use a digital wave pattern in the first lightvolume and a linear intensity pattern in the second volume and aconstant amount of light in a third pattern as shown in FIG. 6 bywaveforms 60, 61 and 62, respectively. In this case projector angle canbe found by using ratios A/C and B/C found in FIG. 6 as addressarguments for finding projector angle in a look up table.

In another embodiment of the present invention, the light projector maybe moved along the surface while the light intensity is varied. On theother hand, the light intensity may be held constant while the lightprojector is moved along the surface at variable speed. The variation inspeed can be carried out by applying mechanical rotation or using a mashhaving an LCD or PZLT array.

In another embodiment of the present invention, a projector constructedas shown in FIG. 7 can transmit approximately linear sloped intensityvolumes as shown in FIGS. 1 and 1A. Light source 70 transmits light andpart of this light is collected by condenser lens 71 and transmitted tofocal plane mask 73. Light passing through mask 73 is focused byprojector lens 72 to the focused pattern region 74. Details of buildingsuch a projector is well understood by those skilled in optical systemdesign. The unique feature of this projector arrangement is that itgenerates approximately the waveform shown in FIGS. 1 and 1A. Deviationsin the output of FIGS. 1 and 1A can be tolerated by calibration. Togenerate this waveform the rotating mask 73 chops the light while thecamera integrates the light output which is low on one side of thevolume and high on the other side of the volume, while the choppedoutput is going from off to on. The opposite waveform is generated whilethe chopped output goes from on to off. The waveform is illustrated inFIG. 7A.

A constant amount of light can be added to each camera picture asillustrated in FIG. 7B. This may be necessary to ensure sufficientsignal strength to reliably process. Two methods disclosed by thisinvention are:

1. When region d1=d2 and region d2 is only partially opaque on mask 73.

2. When region d1>d2. Opaque region d2 is made just wide enough to equalthe focal plane aperture width so that the light is completely blocked.Open region d1, being wider than the aperture width, will allowadditional light to pass.

FIG. 7A shows graphically the integrated light intensity as a functionof horizontal position in the projected pattern when the black region ofthe mask is opaque, and d₁ =d₂. d₁ and d₂ are horizontal distances. Theinterval t₁ is the period of time for the image of the opaque mask edgeto travel across the projected pattern width, t₁ =f (rotational speed).In FIG. 7A, the interval t₁ is equal to t₂.

FIG. 7B shows graphically the condition when region d₁ is greater thand₂ or when the region, d₂, is partially opaque, and t₁ =t₂. In FIGS. 7Aand 7B, the camera recording frame is taken separately during t₁ andduring t₂.

When carrying out the method in accordance with the configuration inFIGS. 1 and 1A, in which volume 14 has light intensity varying in ahorizontal direction, the camera 18 is displaced horizontally and angledsuch that its in-focus view coincides with the projected light at thesurface to be measured.

An alternate method of providing the horizontally varying lightintensity patterns will now be described. It has the particularlyadvantageous property of enabling more uniform vertical intensity whichis necessary for accurate results when using the method of differencesof intensities mentioned above.

A horizontal plane of light having the required horizontal lightintensity modulation described previously for volumes 14 and 26 in FIGS.1 and 1A is projected on the surface 12 containing point 11 to bemeasured. The camera can record the line of intersection of the surfaceand the plane of light starting parallel to the top of light volume 14impinging on the surface 12, and thereafter that line is lowered andanother photograph is taken by the camera. This procedure of loweringthe line and taking a sequential series of photographs would ordinarilybe necessary to acquire the necessary projector angle information. Toavoid the necessity of taking numerous such photographs by the camera,the present invention provides further that the camera shutter remainsopen while the line is moved vertically. With this procedure, the cameraintegrates all these lines and the resulting effect is that theinformation in an area of the surface is obtained. This procedure alsodoes not require a mask except for the line.

While most of the previous examples deal with varying intensity planesand volumes of light (horizontal or vertical) the method is alsoapplicable to two dimension light patterns (checker board patterns,etc.). FIG. 9, shows an example of a pattern that varies in twodimensions. Neither is the orientation of the system critical to theessence of the invention although the camera and projector orientationwithin the invention is critical. In FIG. 9 the volume of light 90emitted by the projector 93 is seen to vary in two dimensions 91 and 92.

Further, it is possible to remove ambiguities such as those caused byreflections, by recording the same light patterns with a camera from adifferent aspect angle and then rejecting all measured values that theprocessed data from the two cameras do not agree to lie at the samephysical location.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention,and therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed is:
 1. A method for determining projector angles topoints on a surface to provide three-dimensional position information onsaid points, comprising the steps of: irradiating selectively a surfacewith irradiating volumes having varying intensities defining a firstpattern; irradiating said surface with irradiating volumes havingvarying intensities defining at least a second pattern; a point to belocated on the surface being irradiated by said first and at least saidsecond patterns; recording images of said patterns; and scanning saidimages to find the intensities of said point in the at least twopatterns, said point having a possible location where the recordedimages have equal values as well as at locations between points wherethe recorded images have equal values, whereby three-dimensionalmeasurements of points are obtained for an entire region between pointsof equal values of intensity as well as at points of equal values ofintensity; the determination of projector angle to said point on thesurface being dependent on a predetermined algebraic function of theintensities of said point in said at least two patterns, saidintensities having calibrated singlevalued algebraic functions.
 2. Amethod as defined in claim 1, wherein said first pattern and at leastsaid second pattern are linear functions.
 3. A method as defined inclaim 1, wherein said algebraic function is a ratio of the intensitiesof said point in said at least two patterns.
 4. A method as defined inclaim 1, wherein said algebraic function is the difference of theintensities of said point in said at least two patterns.
 5. A method asdefined in claim 1, wherein at least said first pattern is a sinusoidalfunction and at least said second pattern is a linear function.
 6. Amethod as defined in claim 1, wherein said first pattern and at leastsaid second pattern are sinusoidal functions displaced in phase.
 7. Amethod as defined in claim 1, wherein said first pattern and at leastsaid second pattern are sinusoidal functions of different frequencies.8. A method as defined in claim 1, wherein said first pattern and atleast said second pattern are non-smooth functions.
 9. A method asdefined in claim 1, wherein said images of said patterns are recorded bya camera with a shutter, and moving said patterns while holding open theshutter of the camera.
 10. A method as defined in claim 1, wherein saidfirst pattern and at least said second pattern are two dimensionalfunctions.
 11. A method as defined in claim 1, wherein said firstpattern is a digital pattern and at least said second pattern is alinear function.
 12. A method as defined in claim 9, wherein said imagesof said patterns are generated by a horizontal light pattern containedin a line of light which is moved vertically while the camera shutter iseither opened for each vertical position of the line or left open topermit integration of the line positions, for producing a controlledhorizontal light intensity variation free of vertical intensityvariation.
 13. A method as defined in claim 9, wherein said images andsaid patterns are generated by moving a uniformly illuminated verticalline of light horizontally at a constant rate while the projectorchanges the brightness of the line of light and the camera integratesthe surface image.
 14. A method as defined in claim 9, wherein thebrightness is kept constant and the rate of movement changes to effectthe amount of light integrated by the camera.
 15. A method as defined inclaim 9, wherein said images of said patterns are generated by moving anat least partially opaque shutter in the projector focal plane so thatthe integrated light varies controllably from one side of the lightvolume to the other.
 16. A method as defined in claim 1, wherein saidfirst pattern and at least said second pattern have different spectralfrequencies which may simultaneously irradiate the surface and thereflected signals are separated by filters.